Prevention of iatrogenic inferior alveolar nerve injuries in relation to dental procedures

This article aims to review current hypotheses on the aetiology and prevention of inferior alveolar nerve (IAN) injuries in relation to dental procedures. The inferior alveolar nerve can be damaged during many dental procedures, including administration of local anaesthetic, implant bed preparation and placement, endodontics, third molar surgery and other surgical interventions. Damage to sensory nerves can result in anaesthesia, paraesthesia, pain, or a combination of the three. Pain is common in inferior alveolar nerve injuries, resulting in significant functional problems. The significant disability associated with these nerve injuries may also result in increasing numbers of medico-legal claims. Many of these iatrogenic nerve injuries can be avoided with careful patient assessment and planning. Furthermore, if the injury occurs there are emerging strategies that may facilitate recovery. The emphasis of this review is on how we may prevent these injuries and facilitate resolution in the early post surgical phase. CLINICAL RELEVANCE: It is imperative that dental practitioners are aware of the significant disability associated with iatrogenic nerve injuries and have an awareness of risk factors relating to inferior alveolar nerve injury. By understanding the risk factors and modification of intervention as a result, more of these injuries will be prevented.     

Frequency of trigeminal nerve injuries following third molar removal.

PURPOSE: To estimate oral and maxillofacial surgery reporting of the frequency of temporary and permanent inferior alveolar and lingual nerve damage from lower third molar extraction and injury etiology, and to identify factors associated with injury rates. MATERIALS AND METHODS: A postal survey was sent to all members of the California Association of Oral and Maxillofacial Surgeons requesting information on known instances of inferior alveolar and lingual nerve damage that had occurred in their practices over a 12-month period and known instances of permanent damage over their entire careers. RESULTS: Replies were obtained from 535 California Oral and Maxillofacial Surgeons (OMFS) representing 86% of all OMFS in California. Instances of injury to the inferior alveolar nerve in a 12-month period were reported by 94.5% of OMFS; 53% reported instances of lingual nerve injury in a 12-month period. Instances of permanent nerve injury of the inferior alveolar nerve were reported by 78% of OMFS; 46% reported permanent lingual nerve injury occurring during their professional lifetime. The overall estimated self-reported rate of injury was 4 per 1,000 lower third molar extractions for the inferior alveolar nerve and 1 per 1,000 extractions for the lingual nerve for all cases (temporary and permanent). In most cases (80%) of inferior alveolar nerve injury the cause was known, but in a majority of cases of lingual nerve injury (57%) the injury etiology was unknown. Self-reported rates of permanent injury were 1 per 2,500 lower third molar extractions for the inferior alveolar nerve and 1 per 10,000 lower third molar extractions for the lingual nerve. Injury rates were associated with provider experience (ie, extractions per year) and years in practice. CONCLUSION: This survey included a high percentage of California OMFS. Injury to the inferior alveolar and lingual nerve was reported by most OMFS in California following lower third molar removal, and many reported cases of permanent nerve injury, frequently with unknown cause.     

Use of dental panoramic tomographs to predict the relation between mandibular third molar teeth and the inferior alveolar nerve. Radiological and surgical findings, and clinical outcome

OBJECTIVES: To compare preoperative radiological observations from dental panoramic tomographs (DPT), with surgical findings at removal of third molars with respect to the inferior alveolar nerve. STUDY DESIGN: One surgeon viewed the radiographs of 219 patients and recorded the radiological observations of the mandibular third molar tooth and the inferior alveolar nerve. The same surgeon removed the teeth and made detailed records of morphology of the root and its relation to the inferior alveolar nerve. Patients were reviewed postoperatively. RESULTS: A total of 300 teeth were removed and the neurovascular bundle was directly observed the root was grooved, or roots apices were deflected by the bundle in 35 (12%) cases. Postoperatively no patient had altered labial sensation. CONCLUSION: There was an intimate relation between the mandibular third molar tooth and the inferior alveolar nerve in 12 (51%) cases when darkening of the root was observed, and in only 11 (11%) cases when interruption of the radiopaque outline of the inferior alveolar neurovascular bundle was observed.     

Lingual nerve damage due to inferior alveolar nerve blocks: a possible explanation

BACKGROUND: An explanation for the predominance of injuries to lingual nerves over those to inferior alveolar nerves as a result of inferior alveolar nerve blocks may be due to the nerves' fascicular pattern. A unifascicular nerve may be injured more easily than a multifascicular nerve. METHODS: The authors unilaterally dissected lingual and inferior alveolar nerves from 12 cadavers. They cut the specimens 2 millimeters above the lingula for both the lingual nerve and inferior alveolar nerve and opposite the site of the middle of the third molar for the lingual nerve, and they counted the number of fascicles at each site. RESULTS: For the lingual nerve at the lingula, the mean number of fascicles was three (range, one to eight). Four of the 12 nerves (33 percent) were unifascicular at this point. Opposite the third molar, the lingual nerve had a mean of 20 fascicles (range, six to 39). In every case, there were more fascicles in the third molar region than above the lingula in the same nerve. At the lingula, the inferior alveolar nerve had a mean of 7.2 fascicles (range, three to 14). CONCLUSION: This study may explain the observation that when an inferior alveolar nerve block causes permanent nerve impairment, the lingual nerve is affected about 70 percent of the time and the inferior alveolar nerve is affected only 30 percent of the time. In 33 percent of cases, the lingual nerve had only one fascicle at the lingula; a unifascicular nerve may be injured more easily than a multifascicular one. CLINICAL IMPLICATIONS: There is no known way to avoid the remote possibility of nerve damage resulting from an inferior alveolar nerve block. The lingual nerve may be predominantly affected because of its fascicular pattern.     

Efficacy and complications associated with a modified inferior alveolar nerve block technique. A randomized,triple-blind clinical trial

Objectives: To compare the efficacy and complication rates of two different techniques for inferior alveolar nerve blocks (IANB). Study Design: A randomized, triple-blind clinical trial comprising 109 patients who required lower third molar removal was performed. In the control group, all patients received an IANB using the conventional Halsted technique, whereas in the experimental group, a modified technique using a more inferior injection point was performed. Results: A total of 100 patients were randomized. The modified technique group showed a significantly higher onset time in the lower lip and chin area, and was frequently associated to a lingual electric discharge sensation. Three failures were recorded, 2 of them in the experimental group. No relevant local or systemic complications were registered. Conclusions: Both IANB techniques used in this trial are suitable for lower third molar removal. However, performing an inferior alveolar nerve block in a more inferior position (modified technique) extends the onset time, does not seem to reduce the risk of intravascular injections and might increase the risk of lingual nerve injuries. Key words:Dental anesthesia, inferior alveolar nerve block, lidocaine, third molar, intravascular injection.     

Iatrogenic trigeminal post-traumatic neuropathy: a retrospective two-year cohort study

With the growing demand for dental work, trigeminal nerve injuries are increasingly common. This retrospective cohort study examined 53 cases of iatrogenic trigeminal nerve injury seen at the Department of Oral and Maxillofacial Surgery, University Hospitals of Leuven between 2013 and 2014 (0.6% among 8845 new patient visits). Patient records were screened for post-traumatic trigeminal nerve neuropathy caused by nerve injury incurred during implant surgery, endodontic treatment, local anaesthesia, tooth extraction, or specifically third molar removal. The patients ranged in age from 15 to 80 years (mean age 42.1 years) and 68% were female. The referral delay ranged from 1 day to 6.5 years (average 10 months). The inferior alveolar nerve (IAN) was most frequently injured (28 cases), followed by the lingual nerve (LN) (21 cases). Most nerve injuries were caused during third molar removal (24 cases), followed by implant placement (nine cases) and local anaesthesia injuries (nine cases). Pain symptoms were experienced by 54% of patients suffering IAN injury, compared to 10% of patients with LN injury. Persistent neurosensory disturbances were identified in 60% of patients. While prevention remains the key issue, timely referral seems to be a critical factor for the successful treatment of post-traumatic neuropathy.     

Leukaemic infiltration of the mandible in a young girl

BACKGROUND: This report presents a case of leukaemic infiltration of the mandible in a 10-year-old female of Sudanese extraction. CASE REPORT: The patient was in remission from acute lymphoblastic leukaemia when she presented with pain localized to the alveolar ridge overlying the unerupted lower right second permanent molar. Two days later, she developed right inferior alveolar nerve paraesthesia. Radiographic imaging demonstrated cortical line absence around the developing lower right second and third permanent molars, and distal displacement of the lower right third molar. In addition, the cortical outline of the right inferior dental canal lacked clarity. Biopsy confirmed leukaemia recurrence demonstrating the Philadelphia chromosome. Tailored chemotherapy was commenced, and a bone marrow transplant was carried out 12 weeks later. At 6-month dental review, the patient remained exceptionally well with no bone pain and normal sensation in the right lower lip. CONCLUSION: The importance of regular and long-term dental examination of patients with leukaemia is discussed.     

微创拔除压迫下牙槽神经的第三磨牙方法分析

目的: 应用牵引拔牙、截冠和超声骨刀微创拔牙技术拔除压迫下牙槽神经的第三磨牙,观察术后产生下唇麻木等并发症的发生情况。方法: 选择60例全景片和锥形束CT（CBCT）显示下颌第三磨牙牙根压迫下牙槽神经的患者,分别采用3种方法拔牙各20例,术后检查下唇麻木情况。结果: 应用牵引拔牙技术和截冠方法拔除压迫下牙槽神经的第三磨牙,术后无人发生下唇麻木,而应用超声骨刀微创拔牙的患者中有1例出现轻微的下唇麻木症状,经用药1个月后好转。结论: 牵引拔牙技术、截冠和超声骨刀3种方法均可有效避免智牙拔除后下唇麻木的并发症。     

Inferior alveolar nerve damage because of overextended endodontic material: a problem of sealer cement biocompatibility?

Damage to the inferior alveolar nerve is a relatively infrequent complication in dental practice. When root canal treatment of a lower molar or premolar surpasses and/or overextends beyond the apical foramen and invades the periapical zone, the foreign material introduced within such a sensitive anatomical space may mechanically or even chemically affect the inferior alveolar nerve. We describe a case of endodontic treatment of a permanent right lower first molar in which the sealer cement overextended in large amounts and damaged the right inferior alveolar nerve. The condition reverted a few months after the surgical removal of the material. Evaluation of the removed material, using powder x-ray diffraction and scanning electron microscopy with coupled dispersive energy spectroscopy, showed it to consist of calcium tungstate (scheelite [CaWO4]) and zirconium oxide (baddeleyite [ZrO2]), which were chemical components of the sealer cement.     

Evaluation of trigeminal nerve injuries in relation to third molar surgery in a prospective patient cohort. Recommendations for prevention

Trigeminal nerve injury is the most problematic consequence of dental surgical procedures with major medico-legal implications. This study reports the signs and symptoms that are the features of trigeminal nerve injuries caused by mandibular third molar (M3M) surgery. 120 patients with nerve injury following M3M surgery were assessed. All data were analysed using the SPSS statistical programme and Microsoft Excel. 53 (44.2%) inferior alveolar nerve (IAN) injury cases and 67 (55.8%) lingual nerve injury (LNI) cases were caused by third molar surgery (TMS). Neuropathy was demonstrable in all patients with varying degrees of paraesthesia, dysaesthesia (in the form of burning pain), allodynia and hyperalgesia. Pain was one of the presenting signs and symptoms in 70% of all cases. Significantly more females had IAN injuries and LNIs (p < 0.05). The mean ages of the two groups of patients were similar. Speech and eating were significantly more problematic for patients with LNIs. In conclusion, chronic pain is often a symptom after TMS-related nerve injury, resulting in significant functional problems. Better dissemination of good practice in TMS will significantly minimize these complex nerve injuries and prevent unnecessary suffering.     

Inferior alveolar nerve damage after lower third molar surgical extraction: a prospective study of 1117 surgical extractions

PURPOSE: The purpose of this study was to determine the incidence of inferior alveolar nerve (IAN) damage after surgical removal of lower third molars, to identify the causes, and to construct a predictive model to assess the risk of IAN injury. STUDY DESIGN: We performed a nonrandomized forward prospective study of 946 consecutive outpatients subjected to surgical extraction of 1117 lower molars in the University of Barcelona Oral Surgery Department. Preoperative, intraoperative, and postoperative data were gathered, and suspected causal factors of IAN damage were identified by using nonparametric tests, the Pearson chi-square test, and the Fisher exact test. Logistic regression predicted the risk of IAN injury. RESULTS: Although only 1.3% of the extractions caused temporary nerve damage, 25% of the lesions were permanent. All of the following significantly increased the risk of IAN damage (P < .05): age, the radiologic relationship between the apices and the mandibular canal, deflection of the root when approaching the mandibular canal, distal ostectomy, the distance of the apices of the third molar to the mandibular canal, ostectomy, crown sectioning, pain during root luxation, primary closure of the wound, prolonged operating time, bleeding, exposure of the nerve, and postoperative ecchymosis. The first 4 factors were included in a predictive logit model. CONCLUSIONS: Patient age, ostectomy of the bone distal to the third molar, the radiologic relationship between the roots of the third molar and the mandibular canal, and deflection of the mandibular canal increased the risk of IAN damage. Older patients were at a higher risk for suffering permanent injuries.     

Gow-Gates法下牙槽神经阻滞麻醉在下颌阻生第三磨牙拔除术中的麻醉效果研究

目的 通过临床随机对照试验的方法评价Gow-Gates法下牙槽神经阻滞麻醉在下颌阻生第三磨牙拔除术中的麻醉有效性和安全性。方法 使用左右半口设计,32例患者的左右下颌阻生第三磨牙分别随机采用Gow-Gates法和传统注射法进行下牙槽神经阻滞麻醉,并拔除下颌阻生第三磨牙,记录麻醉效果及不良事件。结果 所有患者均完成研究。Gow-Gates法的麻醉成功率为96.9%,传统注射法的麻醉成功率为90.6%,二者的麻醉成功率无统计学差异（P=0.317）。在麻醉程度上,Gow-Gates法麻醉程度为A和B级的比率为96.9%,明显好于传统注射法的78.1%（P=0.034）。Gow-Gates法的回抽出血率明显低于传统注射法（P=0.025）,2种注射方法均未出现血肿。结论 Gow-Gates法下牙槽神经阻滞麻醉在下颌阻生第三磨牙拔除术中的麻醉效果好且较为安全,可以作为传统注射法的有效补充。     

Anatomical differences in lower third molars visualized by 2D and 3D X-ray imaging: clinical outcomes after extraction

The purpose of this study was to evaluate the relationship between third molars and the inferior alveolar canal using panoramic radiographs and cone beam computed tomography (CBCT) scans and to assess clinical outcomes after third molar removal retrospectively. The degree of superimposition, buccolingual position (buccal, central, and lingual) and physical relationship (separation, contact, and involved) were measured using CBCT scanning. Post-extraction complications were recorded. Based on radiographic evaluation, 45.9% of third molar roots were inside the inferior alveolar canal, 21.3% were in contact with the inferior alveolar canal, and 32.8% were separated from the canal. The frequency at which the mandibular canal was separated from the root apex was significantly higher when the canal was in the buccal position (80.0%) than in the central (20.0%) and lingual positions (0.0%). Although on panoramic radiographs all third molars were directly superimposed on the inferior alveolar canal, CBCT showed direct contact or canal involvement in 67.2% and separation of the canal from the root apex in 32.8%. Complications occurred in nine patients: eight had third molar root apices inside or in contact with the inferior alveolar canal. The prevalence of post-extraction complications correlated with the absence of cortication around the inferior alveolar canal.     

Influence of the tooth section technique in alveolar nerve damage after surgery of impacted lower third molars

This study is a randomized control split-mouth non-blinded prospective trial, the aim of which was to evaluate clinically the frequency and type of injury to the inferior alveolar nerve (IAN) following mandibular third molar surgery using or not using the tooth section technique. The sample consisted of 50 lower third molars in 25 patients, in the control group the tooth section technique was not used, and it was used in the experimental group. The outcomes have shown a frequency of 8% of IAN injury for both groups (in both genders), and there were no statistically significant associations between the use of the tooth section technique and a diminished incidence of IAN injury or the presence of radiographic signs of a direct relationship between the tooth/nerve/mandibular canal and IAN injury. There was no association between deformities of the tip of dental needles and nerve injury. Temporary hypoesthesia and paresthesia were the commonest nerve injuries. All patients recovered from these injuries within six months.     

累及下牙槽神经的下颌第三磨牙拔除方法研究进展

 累及下牙槽神经的下颌第三磨牙传统拔除方法常会引起以下牙槽神经损伤为主的并发症,为此有众多学者提出新的拔除方法,如截冠法、正畸牵引辅助及冠周去骨法等,以减少下牙槽神经损伤的发生。文章就累及下牙槽神经的下颌第三磨牙拔除方法的原理、适应证、操作注意事项及优缺点等做一综述。     

Clinical characteristics of trigeminal nerve injury referrals to a university centre

The aim of this retrospective study was to determine the aetiology and characteristics of trigeminal nerve injuries referred to a university centre with nerve injury care. Fifty-nine patients with 73 injured trigeminal nerves were referred in 10 months. The most common aetiologies were odontectomy (third molar surgery) (52.1% of nerves), local anaesthetic (LA) injections (12.3%), orthognathic surgery (12.3%) and implant surgery (11.0%). The inferior alveolar nerve (IAN) was most commonly injured nerve (64.4%), followed by the lingual nerve (LN) (28.8%). About a quarter of IAN injuries (27.3%) and half of LN injuries (57.1%) from odontectomy had severe sensory impairment. There were twice as many LN than IAN injuries from local anaesthetic injections, but all had mild or no sensory impairment. Nerve injuries from implant surgery occurred only in IAN injuries; none had severe sensory impairment. Neuropathic pain occurred in 14.9% of IAN injuries and only in those with mild or no sensory impairment. Nerve surgery was offered to 45.8% of patients; a third underwent surgery.     

累及下牙槽神经的下颌第三磨牙拔除方法研究进展

累及下牙槽神经的下颌第三磨牙传统拔除方法常会引起以下牙槽神经损伤为主的并发症，为此有众多学者提出新的拔除方法，如截冠法、正畸牵引辅助及冠周去骨法等，以减少下牙槽神经损伤的发生。文章就累及下牙槽神经的下颌第三磨牙拔除方法的原理、适应证、操作注意事项及优缺点等做一综述。     

Inferior alveolar nerve injury caused by thermoplastic gutta-percha overextension

Injuries to the inferior alveolar nerve following trauma resulting in a mandibular fracture are well documented and are a well-known risk when surgical procedures are planned for the mandible in the region of the inferior alveolar canal. Such injuries are relatively rare following endodontic therapy. This article reports a case of combined thermal and pressure injury to the inferior alveolar nerve, reviews the pathogenesis of such an injury and makes suggestions for its management.     

牵引拔除压迫下牙槽神经的下颌第三磨牙

目的：应用牵引技术拔除压迫下牙槽神经的下颌第三磨牙,以减少术后并发症。方法：对20例全景片和CT显示下颌第三磨牙牙根压迫或紧贴下牙槽神经的患者,先应用正畸牵引技术牵引,经3～10周的牵引,使牙根远离下牙槽神经后再行拔除术。结果：20例牙根压迫下牙槽神经的患者,经牵引拔牙后,无1例发生下唇麻木,术后反应轻微。结论：应用牵引拔牙技术拔除下颌第三磨牙,解决了术后下唇麻木、骨折等高风险并发症的发生,也使拔牙更容易、更快。     

Inferior alveolar nerve injury and surgical difficulty prediction in third molar surgery: the role of dental panoramic tomography

OBJECTIVE: The purpose of this study was to evaluate the relationship between preoperative panoramic radiological findings and postoperative inferior alveolar nerve paresthesia following third molar surgery, and to assess the surgical difficulty. METHODOLOGY: This retrospective study involved two groups of patients who were randomly selected. The first group presented with inferior alveolar nerve (IAN) paresthesia following surgery, and the second group presented with no complications, including IAN paresthesia. Radiological findings were collected from the panoramic radiographs of those patients and compared to postoperative paresthesia. The degree of surgical difficulty was also assessed radiographically. RESULTS: The application of Chi-square testing on the numbness group and the control group, as well as the numbness group (two years postoperatively) and the control group, showed that parameters like type of impaction (fully impacted), depth of impaction (depth C), ramus/space (class 3), spatial relationship (distoangular and horizontal), number of roots (multiple and incomplete), shape of root (thick and incomplete), shape of the tip of root (curved and incomplete), and relation to IAN (touching, superimposed, or non-specific) are highly significant (p < 0.001) in predicting the incidence of temporary and permanent paresthesia. Logistic regression showed that a patient whose lower third molar is > or = 1 mm from IAC has a 98% probability of no numbness, while if the tooth is touching the IAC the probability of numbness between one week and < two years is 60%. Numbness probability of darkening of the root is 48% for > two years, deflection of the root has a 42% probability of > two years numbness, narrowing of the root has 87% of numbness between > one month and < two years, a dark and bifid root has a 97% of numbness between > six months and < two years, interruption of the IAC has a 54% chance of numbness between > one month and < two years, diversion of the canal has a 60% probability of > six months to > two years numbness, while narrowing of the canal has a probability of 100% of > six months to > two years numbness. By using logistic regression, cases that were recorded as "very difficult," according to the Pederson Difficulty Index, were more likely to develop permanent paresthesia (95%). The application of logistic regression on the radiological findings showed that we can use them in predicting nerve paresthesia following third molar surgery. A classification tree has been developed and found to be very accurate in predicting permanent numbness (95%) and no numbness (100%) in third molar surgery depending on the radiological findings. CONCLUSION: Surgical difficulty of impacted third molars may be assessed radiographically through seven factors, including spatial relationship, depth of impaction, ramus relationship/space available, type of impaction, number and shape of roots, shape of the tip of the root, and relation of the root to the inferior alveolar nerve. The application of logistic regression on the radiological findings showed that we could use them in predicting nerve paresthesia following third molar surgery. By developing a classification tree, it is easier to predict the possibility of temporary or permanent paresthesia. A full collaboration between clinicians and radiologists may help to uncover more parameters that can lead to a more accurate prediction of temporary and permanent paresthesia.